Fuzzy systems are used to control apparatus such as air conditioners by fuzzy control. In the fuzzy system, fuzzy deductions are carried out in which a deduction rule is defined if adequate results can be obtained by fact information having fuzzy borders. Such fuzzy systems for fuzzy control are classified to two groups, one is controlled by software and the other is controlled by hardware. The fuzzy system controlled by hardware has an advantage in that arithmetic processes are carried out in a higher speed compared with that controlled by software. The fuzzy system controlled by hardware is then classified to analog and digital types.
A conventional analog fuzzy hardware system includes a minimum arithmetic circuit (defined as a MIN arithmetic circuit hereinafter), a maximum arithmetic circuit (defined as a MAX arithmetic circuit hereinafter) and a truncation gate circuit. The MIN arithmetic circuit supplies a data signal having a minimum value selected from a plurality of input data signals. The MAX arithmetic circuit supplies a data signal having a maximum value selected therefrom. The truncation gate circuit carries out a head-cut (.alpha.-cut) process in which a plurality of input signals are cut to have predetermined values if the input signals are over the predetermined value.
A conventional digital fuzzy hardware system includes a basic block consisting of first and second MIN arithmetic circuits each having two input terminals, a MAX circuit and a 3-bit shift register. In the digital fuzzy hardware system, a membership function is used for fuzzy process. The membership function which is a fuzzy set is sampled to provide a plurality of singletons which form a vector. Each singleton is represented by 4-bit binary word consisting of "0" or "1" to represent the grade. The data consisting of the plurality of the 4-bit binary words are processed serially, so that number of stages of the basic blocks are used. In each basic block, first and second clocks which have different phases are used.
In operation, fuzzy word Ai which is the data of the previous stage and the fuzzy word A' which represents the fact information are supplied as every 4-bit word (element) to the first MIN arithmetic circuit in which the elements of the two fuzzy words Ai and A' are compared by serial process in synchronizing with the first clock, and the smaller one is supplied to the MAX arithmetic circuit. In the MAX arithmetic circuit, the supplied element is compared with the one supplied from the 3-bit shift register, and the larger one is supplied to the 3-bit shift register. In the 3-bit register, the supplied element is shifted in turn, and then is supplied to both the MAX arithmetic circuit and the second MIN arithmetic circuit. In the second MIN arithmetic circuit, the supplied element is compared with a corresponding element of a fuzzy word Bi, and the smaller one is supplied as an output. Thus, one deduction process completes by carrying out these processes explained above for 256 clock cycles.
In this example, sixteen deduction processes are carried out simultaneously at sixteen fuzzy deduction engines corresponding to the basic block, respectively. Then, MAX arithmetic process of the results of the sixteen deductions is carried out to be integrated. The MAX arithmetic process thereof is carried out by the MAX arithmetic circuit having two input terminals, so that the results of the sixteen deductions B.sub.1 ', B.sub.2 ', B.sub.3 ', . . . B.sub.16 ' are passed through four stages of MAX trees to obtain the integrated results of the MAX arithmetic process. Accordingly, the final deduction results B' is supplied serially from the output terminal of the MAX tree.
According to the conventional fuzzy hardware system, however, there are disadvantages as explained below. In the conventional analog fuzzy hardware system, the power consumption thereof is large, because many constant current sources are used therein. Such a large power consumption as well as heat generation in elements composing the system may become obstacles to increase of degree of integration. On the other hand, in the conventional digital fuzzy hardware system, the MIN or MAX arithmetic circuit in the basic block has only two input terminals, so that many stages of basic blocks are required. Consequently, the system scale may become large, and it is difficult to combine serial and parallel processes in response to the system scale.